The present invention relates to a construction of a self-healing transmission system and, more particularly, to a self-healing ring switch and a method of controlling it.
At present, a self-healing network is exemplified by the 2-Fiber Bidirectional Line Switched Ring (i.e., 2-Fiber BLSR), the 4-Fiber Bidirectional Line Switched Ring (i.e., 4-Fiber BLSR) and the Unidirectional Path Switched Ring (i.e., UPSR), as disclosed in "Bellcore Technical Advisory TA-NWT-001230, issue 3".
The 2-Fiber BLSR is a system in which the individual nodes are connected through two lines to divide the channel of each line into two halves--a working half and a protection half (its shown in FIG. 3A). With the ordinary path, the forward and backward communications pass through the same lines (as shown in FIG. 3B). If the lines 30-4 and 31-4 between nodes A-B fail, for example, in the network shown in FIGS. 3A and 3B, the path through the failed section is bypassed (or ring-switched) by using a counter protection channel (as shown in FIG. 4). What ring-switches at this time is the failed end nodes (i.e., the nodes A and B0 in this example). The remaining nodes execute the relaying of the bypass traffic. The node construction is exemplified in FIG. 5. Each node is equipped with not only in-ring inter-node connecting lines but also a tributary traffic add line 11 and a drop line 12. In case this construction is applied to the node A of FIG. 3A: a CW-direction working reception line 20 corresponds to the line 30-4 of FIG. 3; a CCW-direction working reception line 22 corresponds to a line 31-1 of FIG. 3A; a CW-direction working transmission line 24 corresponds to a line 30-1 of FIG. 3; and a CCW-direction working transmission line 26 corresponds to the line 31-4 of FIG. 3A. The ring switch in the 2-Fiber BLSR can be easily realized by the TSI (i.e., Time Slot Interchange) function belonging to a switch 34-1 in the node. The 4-Fiber BLSR is equipped with working lines and protection lines and connects the individual nodes through four lines. Moreover, the 4-Fiber BLSR normally transmits the working lines but heals the traffic in case a failure occurs by using the protection lines (as shown in FIG. 6A). With the normal path setting, the forward and backward communications pass through the same lines (as shown in FIG. 6B). If only the working line 30-4 between the nodes A-B fails, for example, in the network shown in FIG. 6A, the path through the failed section is effected by using a protection line 32-4 (as span-switched in FIG. 7A). If both the working line and the protection line between the nodes A-B fail, on the other hand, the path through the failed section is bypassed (or ring-switched) through the counter protection line (as shown in FIG. 7B). What executes the span-switching and the ring-switching is the failure end node (as exemplified by the nodes A and B in the present example). The remaining nodes execute the relaying of the bypass traffic. An example of the node construction is shown in FIG. 8. In case this construction is applied to the node A of FIG. 6A: the CW-direction working reception line 20 corresponds to the line 30-4 of FIG. 6A; a CW-direction protection reception line 21 corresponds to the line 32-4 of FIG. 6A; the CCW-direction working reception line 22 corresponds to the line 31-2 of FIG. 6A; a CCW-direction protection reception line 23 corresponds to a line 33-1 of FIG. 6A; the CW-direction working transmission line 24 corresponds to the line 30-1 of FIG. 6A; a CW-direction protection transmission line 25 corresponds to a line 32-1 of FIG. 6A; the CCW-direction working transmission line 26 corresponds to the line 31-4 of FIG. 6A; and a CCW-direction protection transmission line 27 corresponds to a line 33-4 of FIG. 6A. Like the 2-Fiber BLSR, each node is equipped with not only the in-ring inter-node connecting lines, but also the tributary traffic add line 11 and the drop line 12.
The UPSR has its nodes connected through two lines--one for working and the other for protection (as shown in FIG. 9A). With the ordinary path setting, therefore, the forward and backward communications pass through different paths (but in the same direction) (as shown in FIG. 9B). In FIG. 9B, the counter clockwise (i.e., CCW) paths are working so that they are normally used for the transmissions. The clockwise (i.e., CW) paths are for protections. The paths are set for both the working and protection operations, and the working paths are selected at the path terminal node. If a failure occurs between the nodes A-B in FIG. 9A, it can be healed by selecting the protection path at the path terminal node (as shown in FIG. 10). The node construction is shown in FIG. 11. In case this construction is applied to the node A of FIG. 9A: the CW-direction protection reception line 21 corresponds to the line 32-4 of FIG. 9A; the CCW-direction working reception line 22 corresponds to the line 31-1 of FIG. 9A; the CW-direction protection transmission line 25 corresponds to the line 32-1 of FIG. 9A; and the CCW-direction working transmission line 26 correspond to the line 31-4 of FIG. 9A. Output highways 15-5 and 15-7 corresponds to the working and protection ones, respectively. The selection of the working and protection is carried out by a selector 2. Each node is equipped with not only the in-ring inter-node connecting lines, but also the tributary traffic line 11, the drop line 12 and the protection ones.